There are many resources available on the internet that provide more information about web site accessibility and how web sites can be made more accessible.
The World Wide Web Consortium (W3C) is the global authority on accessible design and coding standards:
https://www.w3.org/
W3C offer a range of resources through their Web Accessibility Initiative including guidelines and checklists that web site authors should adhere to:
https://www.w3.org/WAI/
https://www.w3.org/WAI/Resources/
Standards for mobile optimised and responsive web sites can be viewed at:
https://www.w3.org/WAI/mobile
The Equality Act 2010 includes UK Equality legislation:
http://www.legislation.gov.uk/ukpga/2010/15/contents
Read about steps taken to ensure content on Gov.uk is as accessible as possible:
https://www.gov.uk/help/accessibility
The Government Digital Service (GDS), part of the Cabinet Office, is leading the digital transformation of government and services:
https://www.gov.uk/government/organisations/government-digital-service
The BBC offer archived information about ways in which web sites can be customised to make content more accessible:
http://www.bbc.co.uk/accessibility
WebAIM are an authority on web site accessibility. They run email discussion lists and visitors can subscribe to their newsletter service:
http://webaim.org/intro
http://webaim.org/community
Apple provide information about settings within their devices to enhance accessible:
https://developer.apple.com/accessibility/ios